Since "Bookshop Memories" is a reminiscence of a real part of George Orwell's life, it is true that in one sense the memory is the thesis. In another sense, it might be said that Orwell's thesis is the exploration into the psychology of customers who frequent the bookshop, a second hand bookshop and therefore more accessible to those of limited income, and also make use of the shop's lending library.
Orwell has rather severe things to say about women of vague mindedness, people who are first edition "snobs," the slightly maladjusted who enjoy ordering expensive books for no purpose whatsoever having no intention of purchasing them (or--according to Orwell--of stealing them), and other regular bookshop types. [One thinks of the customer in the film Notting Hill who insists on lackadaisically asking for fiction in a travel book store.]
Orwell found that what he calls a person's true taste is exposed in a lending library and that it conflicts with their pretentious taste put on for show. But in another sense, Orwell's conclusion--based as it is on his descriptions of the frequenters of a second bookshop--that he wouldn't want to run a bookshop may be his final thesis.